This invention relates to hermetically sealed compressors.
In particular, this invention relates to an improved plastic suction muffler configuration for hermetically sealed compressors of the reciprocating type.
Hermetically sealed compressors also known as hermetic compressors are used to compress low-pressure vapor from an evaporator and deliver high pressure and high temperature vapor to a condenser.
Such hermetically sealed compressors of the reciprocating-type, usually consist of a motor-compressor unit mounted within a hermetically sealed shell. Such compressors have an electric motor-driven piston reciprocating in a cylinder at relative high speeds of 3000 to 4000 r.p.m., which draws in and compresses a refrigerant fluid.
The hermetically sealed compressor generally comprises a lower and upper shell, inside which three or more resilient members hold the pump assembly (coil springs). The whole assembly body is supported by legs, which are attached to the lower shell. The pump assembly consists of a motor component stator and rotor and a refrigerant fluid compressor mechanism. The rotor is fitted directly on the crankshaft. The crankshaft is housed in the main bearing provided in the crankcase. The stator is mounted on the crankcase through fasteners. The power required for rotation of the crankshaft is given by the motor.
The reciprocating movement of the piston causes intermittent flow of refrigerant fluid through valves. This intermittent flow of fluid through the system causes undesirable levels of noise. The reciprocating mechanism used to compress the refrigerant also generates a lot of high frequency series of pulses which if allowed to act directly on the refrigerant fluid cavity leads to vibration of the compressor and/or generates more noise in the audible frequency range. Usually a pulse attenuator /silencer or acoustic dampening system or a muffler becomes necessary on both, the suction and the discharge side of the pumping mechanism to take care of this effect.
In the hermetically sealed refrigeration compressor, refrigerant fluid enters through the suction tube and travels into the shell, which surrounds the pump assembly. The refrigerant fluid is further picked up by the suction pick up tube and led into the crankcase, which then goes into the suction plenum in the cylinder head through suction mufflers, which are in built in the crank case. Inside, the motor and pump assembly are cooled by refrigerant available inside the shell cavity. In this process the refrigerant fluid picks-up heat from these (motor and pump assembly) hotter components before it reaches in to the crankcase by heat convection. It is well known from basics of thermodynamics that refrigerant fluid super heating will result in reduced compressor performance as density of refrigerant fluid reduces with increased temperature which means less mass flow rate in to the cylinder bore.
Generally the suction and discharge mufflers are in built in the crankcase, which is of a highly conductive material, or are fitted as separate metallic components, which are good thermal conductors.
The refrigerant fluid passes through these conventional fluid passages either separate or in built in the crankcase and in so doing picks up heat from the surrounding hotter bodies before it reaches to bore. This is undesirable. There is also a pressure drop of about 1 psi as the refrigerant fluid passes through the muffler. This pressure drop results in decrease in the velocity of the refrigerant fluid and its consequent expansion.
This invention particularly relates to suction mufflers, typically of synthetic polymeric material having thermal insulating characteristics.
Known plastic suction mufflers of the type have a hermetic shell muffler body having an internal chamber and are fitted with a fluid inlet opening and a fluid outlet opening. The fluid inlet fluid outlet opening is in tight communication with the suction valve of the compressor, typically through a suction plenum. In addition to attenuating noise levels the muffler chamber together with the suction plenum also provides an immediate reservoir of refrigerant fluid for the suction stroke of the piston.
In the process of dampening pulses and attenuating noise levels, the prior art mufflers cause a pressure drop because of the flow restrictive property of the muffler chamber into which the refrigerant fluid is led. This pressure drop causes a reduction in the compressor efficiency. Volumetric efficiency of the compressor depends upon compression ratio and clearance volume. Higher suction pressure drop in the muffler will increase the compression ratio and consequently reduce volumetric efficiency of the compressor. Which means that the amount of compressed refrigerant fluid transmitted through the discharge port will be reduced for the same displacement of the piston.
Known prior art suction mufflers are described in U.S. Pat. Nos: 4,370,104; 4,415, 060; 4,582,468; 4,759,693; 4,960,3,68; 5,201,640 and the like.
It is a general object of the invention to provide a suction muffler for reciprocating hermetically sealed compressors which provide attenuation of noise created by the flow and pulsation of the refrigerant fluid and at the same time minimizes the pressure drop across the muffler and thereby reduces the loss in compression or thermal efficiency resulting from the provision of the muffler.
It is an object of the present invention to provide a suction muffler which eliminates the need of a suction plenum in a hermetically sealed compressor.
It is an object of the present invention to provide a new muffler which reduces the effect of superheating of the refrigerant fluid to a great extent.
Another object of the suction muffler is that it is designed such that it results in less pressure drop across it and good attenuation of the suction pulse for a wide band of audible frequencies typically from 0.5 KHz to 3 KHz.
Another object of the invention is to propose a suction muffler which can be directly fitted on the cylinder head by a novel mounting means, eliminating the requirement of a suction plenum between the muffler and the suction valve of the compressor and also eliminating additional clamping means for fitting the suction muffler to the cylinder head.
A particular object of the invention is to provide a suction muffler which is able to suppress low frequency noise [50 to 3000 Hz] generated by refrigerant fluid flow and pulsation.
A still particular object of the invention is to provide a suction muffler in which the refrigerant fluid is led into the muffler with minimum turbulence and reduced pressure drop and traverses the muffler chamber without experiencing any restriction in flow or a sudden change in direction.
According to this invention there is provided a suction muffler for a hermetically sealed compressor of the reciprocating piston type, which comprises a muffling chamber having a body of a synthetic polymeric material and a synthetic polymeric perforated tube passing through the muffling chamber carrying refrigerant fluid from the suction tube of a compressor to the suction port on the valve plate of the cylinder in which a piston reciprocates.
In accordance with another aspect of the invention the said perforated tube is made to diverge at least along part of its length within the muffling chamber.
Plastic mufflers pose their own problems of fitting. A main problem is to fit these plastic mufflers onto the cylinder head.
Such a fitting is required to be stable at various temperatures and withstand vibrations during normal running of the compressor and during transportation. Various types of clamps and bolts, have been resorted to provide for such fittings including xe2x80x98Cxe2x80x99 clamps and xe2x80x98Oxe2x80x99 clamps however these fittings are far from satisfactory.
In the present invention a new method of mounting the plastic suction muffler is developed which avoids additional clamping and bolts for its fitment.
According to still another aspect of this invention therefore, there is provided a method of mounting a muffler directly on the cylinder comprising the steps of:
{i} forming a projection on the muffler tube in the proximity of its outlet end;
{ii} forming a slot on the cylinder head complementary to the projection formed on the muffler tube; and
{iii} mounting the muffler in the cylinder head by press fitting the projection on the muffler tube into the slot in the cylinder head.
Therefore there is provided a hermetically sealed compressor which comprises a motor compressor assembly mounted in a shell which includes a cylinder head and a muffler in which the muffler is fitted to the cylinder head by means of a male projection formed on the muffler tube near its outlet end and a complementary slot formation provided in the cylinder head and clamped over by the pressure of the valve plate.
According to this invention there is therefore provided a hermetically sealed compressor which comprises a motor compressor assembly mounted in a shell which includes a cylinder head and a muffler in which the muffler is fitted to the cylinder head by means of a male projection formed on the muffler tube and a complementary slot formation provided in the cylinder head and clamped over by the pressure of the valve plate.
This invention therefore teaches the concept of making one or more projections on the muffler tube (irrespective of its shape and geometric dimensions) near the outlet of the muffler tube which will directly press fit in to a slot made in the cylinder head which will restrict the muffler movement in the axial or transverse direction as this projection is press fitted in to the cylinder head slot avoiding any other clamping arrangement except the conventional pressure valve plate that fits over the cylinder head.
In accordance with another embodiment of the invention, the projection made on the muffler tube may be further secured by using any adhesive agent, or by any additional clamping arrangement in the cylinder head.
The invention will now be described with reference to the accompanying drawings.